The invention is directed to a drive of a control valve which includes a drive force unit, a yoke for the fixed connection to a valve, a drive spindle for the transmission of the motion of the drive force unit onto the valve and a sensor unit for acquiring the valve position. The sensor unit is integrated in the drive spindle and comprises a magnetic track having a periodic structure, a sensor connected to the yoke of the drive close to the magnetic track with the sensor being suitable for the acquisition of changing magnetic field lines, and at least one magnet in the region of the magnetic track and of the sensor with the magnet having magnetic field lines penetrating both the magnetic track and the sensor.
Such drives, for example, are operated pneumatically, hydraulically or electrically. The drive force unit converts electrical, thermal or mechanical energy into a motion of the drive spindle in order to generate a thrust or a rotation. The sensor unit for measuring the valve position is usually mechanically coupled to the drive spindle. The actual position of the valve can be monitored with the assistance of this sensor unit and can be controlled with a position controller that frequently contains the sensor unit.
Regardless of whether a non-contacting measuring principle such as, for example, a linear armature sensor, an optically incremental sensor or a contacting system such as, for example, conductive plastic is utilized in the sensor unit itself, the motion of the drive spindle is usually converted with a mechanical tap into a motion at a sensor of the sensor unit. The type of mechanical tap and the structure of the position controller for linear motions at drives is described in the standard DIN IEC 534 Part 6. In accord therewith, a connecting member for the return at the drive is provided at the working spindle, this comprising four M6 threaded holesxe2x80x94given rotatability of the connector member, two holes per side sufficexe2x80x94with a bearing area of at least 10 mm diameter for each threaded hole. The mounting material for coupling a position controller to the sensor is co-supplied by the manufacture of the position controller. It usually comprises a lever that is rotatably coupled to the sensor and a dog that is rigidly connected to the drive spindle and engages into the rotatable lever. The attachment of the sensor with the mounting material requires careful assembly and adjustment in order to avoid historesis and in order to correctly select the working range.
On the other hand, EP 0 870 932 A1 discloses a pneumatic or hydraulic cylinder with a cylinder tube, whereby at least one permanent magnet is arranged at a piston, and this magnet uses its magnetic field to actuate at least one signal generator at the outside of the cylinder tube. The signal generator is thereby secured so that it serves as a limit signal generator. The known fastening enables a comfortable displacement and adjustment of the signal generator in order to exactly set the switching points. The shape, nature and arrangement of the permanent magnet, however, is not disclosed.
U.S. Pat. No. 5,670,876 discloses a magnetic position sensor that comprises two magnetic sensors, whereby the one sensor acquires a non-variable flux, and the other sensor measures the modification of the magnetic resistance (xe2x80x9creluctancexe2x80x9d) over the range of measurement. The variable magnetic resistance in that the part whose motion is to be acquired has a specific shape or is connected to an article with such a specific shape, so that the magnetic flux occurs by means of a continuous variation of, for example, the air gap length or the air gap width. The magnetic return has a characteristic shape therefor.
Another magnetic position sensor is disclosed by U.S. Pat. No. 5,359,288 for determining the position of shock absorbers. A Hall sensor thereby measures the strength of a magnetic field as a criterion of the position, and the magnetic region, that moves relative to the hole sensor, is composed of sub-regions having different magnetization, so that the resulting field strength at the Hall sensor continuously varies according to the position.
Magnetic field sensors, particularly magneto-resistive sensors, are likewise known that can be greatly miniaturized. Thus, DE 197 01 137 A1 discloses a length sensor chip whose plane resides opposite a scale plane. Magneto-strictive layer strips having barber pole structures are thereby arranged on the sensor chip in a specific way and fashion in order to be suitable for a high-resolution length measurement with high sensitivity given high resistance.
EP 0 618 373 A1 discloses a drive of the species with a device for determining the position of a magnetizable piston rod in a cylinder relative to a selected reference point. This device comprises a magnet for generating a magnetic field as well as a periodic arrangement of grooves on the piston rod that effect a modulation of the field generated by the magnet. This periodic modulation is sampled via two magnet resistors integrated in a bridge circuit and is electronically processed so that an analog position display is available in addition to the digital and a stroke speed can be read out.
In addition, CH 682 349 A5 discloses a magnetic measurement sensor for acquiring the position, speed and moving direction of a piston or cylinder that detects a flux density change of a magnetic field by means of a periodically profiled, magnetizable piston or cylinder rod. The magnetic flux density is thereby generated via a permanent magnet.
What is disadvantageous about the above devices is that the drive force units for actuators comprise no devices that undertake measures given a power outage in order to enable the continued defined and error-free operation of the actuator or, respectively, to move the actuator, for example in the form of a piston or cylinder rod, into a defined position. Thus, these devices are unsuitable for the control of control valves having high safety demands.
DE 196 21 087 A1 discloses an analog safety circuit for actuators based on RC or, respectively, RL elements that is essentially characterized by two characteristic times. These are thereby a matter of a first, short so-called hold time during which the actuatorxe2x80x94given power outagexe2x80x94is moved into an undefined idle position and of a second, longer hold time during which the actuator is driven into a safe intermediate position in which it should dwell long enough for a service person or an automatic unit to undertake further measures for the protection of a system operated with actuators, particularly measures for further wind-down of the system.
This device also does not enable a defined continued operation of an actuator in the form of a drive in combination with a control valve given interruption of the mains power supply. Further, it can only be utilized for electrically operated actuators.
It is therefore an object of the present invention to develop the drive of the species such that the disadvantages of the prior art are overcome, in particular that a non-electrically operated drive that uses an incremental path sensor system is supplied for a control valve that enables the defined and safe continued operation of the control valve even after outage of an auxiliary energy, for example in the form of a mains power supply.
This object is inventively achieved with an improvement in a drive with a drive force unit, a yoke for the fixed connection to a valve, a drive spindle for the transmission of the motion of the drive force unit onto the valve and a sensor unit for acquiring the valve position, the sensor unit being integrated in the drive spindle and comprising a magnetic track having a periodic structure, a sensor connected to the yoke of the drive close to the magnetic track, the sensor being suitable for the acquisition of changing magnetic field lines, and at least one magnet in the region of the magnetic track and of the sensor, the magnet having magnetic field lines penetrating both the magnetic track and the sensor. The improvements are that the drive is coupled to a control valve, the magnet is a permanent magnet, the sensor can be supplied with energy via an auxiliary energy source, the sensor is connected to a unit for monitoring the electrical auxiliary energy source, the drive includes an energy store for supplying the sensor with electrical energy, the energy store is connected to the sensor at least during an outage of the electrical auxiliary energy, so that the energy store makes it possible to continue the position measurement of the valve position even when outage of the electrical auxiliary energy for at least a characteristic time.
The sensor is connected to a logic circuit which may be in a microprocessor of the sensor and which is connected to a timing unit and generates a signal for the drive unit after a predetermined time when the outage of the electrical auxiliary energy to force the drive spindle into a safe position.
The invention is thus based on the surprising perception that, by offering an energy store in combination with the drive of a control valve for a characteristic or predetermined time, a continued operation of this control valve is enabled by bridging a power outage for a short period of time. For example, with an outage of the auxiliary electrical energy, the control valve is only moved into a safe, defined position after a given, long-lasting outage. After a short-duration outage, the device can thus continue operating without interruption and need not be re-started, i.e. the original position need not be reset such as, for example, by registering initialization data, which in turn proves complex given precision processes upon employment of control valves and cost-intensive due to the time losses that are thereby incurred. All safety reservations in the employment of incremental path sensors in combination with control valves are thus overcome by the invention.